1. Field of the Invention
The present invention relates to a recording head and a recorder, and, for example, to a micro-optical recording head which uses light for information recording and a micro-optical recorder using such a micro-optical recording head, and to an optically assisted magnetic recording head which uses a magnetic field and light for information recording and an optically assisted magnetic recorder using such an optically assisted magnetic recording head.
2. Description of Related Art
In a magnetic recording method, a magnetic bit is remarkably susceptible, at high recording density, to the outside temperature and the like, thus requiring a recording medium having a high coercive force. Use of such a recording medium requires a large magnetic field at recording. The magnetic field generated by the recording head has its upper limit determined by the saturation magnetic flux density, and this value is close to the material limit and thus cannot be expected to increase dramatically. Thus, a method is suggested in which local heating is performed at recording to thereby cause magnetic softening, recording is performed when the coercive force becomes small, then heating is stopped and self-cooling is then attempted to thereby ensure the stability of a recorded magnetic bit. This method is called a heat assisted magnetic recording system.
With the heat assisted magnetic recording method, it is preferable that a recording medium be heated instantaneously. Moreover, contact between a device to be heated and the recording medium are never permitted. Thus, heating is generally performed by use of light absorption, and a method using light for heating is called an optically assisted method. To perform ultra high density recording by the optically assisted method, the required spot diameter is approximately 20 nm, but light cannot be condensed to such a size due to diffraction limitation imposed on a normal optical system. Thus, several methods of heating by using near-field light as non-transmitted light have been proposed (see patent document 1 and the like). In this method, laser light of a suitable wavelength is condensed by an optical system and then irradiated to metal of several tens of nanometers in size (called plasmon probe) to thereby generate near-field light, which is then used as heating means.
[Patent Document 1] JP-A-2005-116155
With a general magnetic recorder (for example, hard disk device), a plurality of recording disks are laid in narrow space with a clearance of 1 mm or below therebetween. Thus, the thickness of a magnetic recording head is limited. The optically assisted magnetic recording head described in patent document 1 and a typical magneto-optic recording head (MO) have a large optical system arranged on the back surface thereof, and thus the magnetic recording head fails to support a magnetic recorder whose magnetic recording head described above is limited in thickness. From this point, very thin light guiding means and condensing means are required for the optically assisted magnetic recording head.
Upon formation of a light spot on the disk by a typical lens or an SIL (solid immersion lens), large NA (numerical aperture) needs to be provided to obtain a small spot size. This means that the angle of rays of light directed to the condensing point is large. An optically assisted section in the optically assisted magnetic recording head needs to exist under the presence of a magnetic recording section and a magnetic reproduction section used in a typical hard disk device; thus, as described above, large NA causes light to interfere with the magnetic recording section and the magnetic reproduction section and also leads to upsizing of the beam diameter and the magnetic recording head.